fw_devlink overlapping cycles fix

This is mainly a bug fix with a additional logging improvement. Lots of details in Patch 2/3.

Thanks,
Saravana

Saravana Kannan (3):
driver core: Fix device_link_flag_is_sync_state_only() driver core: fw_devlink: Improve detection of overlapping cycles driver core: fw_devlink: Improve logs for cycle detection

 drivers/base/core.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

2.43.0.594.gd9cf4e227d-goog

device_link_flag_is_sync_state_only() correctly returns true on the flags of an existing device link that only implements sync_state() functionality. However, it incorrectly and confusingly returns false if it's called with DL_FLAG_SYNC_STATE_ONLY.

This bug doesn't manifest in any of the existing calls to this function, but fix this confusing behavior to avoid future bugs.

---
 drivers/base/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

index 14d46af40f9a..52215c4c7209 100644
@@ -284,10 +284,12 @@ static bool device_is_ancestor(struct device *dev, struct device *target)
 	return false;
 }
 
+#define DL_MARKER_FLAGS		(DL_FLAG_INFERRED | \
+				 DL_FLAG_CYCLE | \
+				 DL_FLAG_MANAGED)
 static inline bool device_link_flag_is_sync_state_only(u32 flags)
 {
-	return (flags & ~(DL_FLAG_INFERRED | DL_FLAG_CYCLE)) ==
-		(DL_FLAG_SYNC_STATE_ONLY | DL_FLAG_MANAGED);
+	return (flags & ~DL_MARKER_FLAGS) == DL_FLAG_SYNC_STATE_ONLY;
 }
 
 /**

2.43.0.594.gd9cf4e227d-goog

fw_devlink can detect most overlapping/intersecting cycles. However it was missing a few corner cases because of an incorrect optimization logic that tries to avoid repeating cycle detection for devices that are already marked as part of a cycle.

Here's an example provided by Xu Yang (edited for clarity):

                    usb
                  +-----+
   tcpc           |     |
  +-----+         |  +--|
  |     |----------->|EP|
  |--+  |         |  +--|
  |EP|<-----------|     |
  |--+  |         |  B  |
  |     |         +-----+
  |  A  |            |
  +-----+            |
     ^     +-----+   |
     |     |     |   |
     +-----|  C  |<--+
           |     |
           +-----+

usb-phy

Node A (tcpc) will be populated as device 1-0050. Node B (usb) will be populated as device 38100000.usb. Node C (usb-phy) will be populated as device 381f0040.usb-phy.

The description below uses the notation:
consumer --> supplier
child ==> parent

1. Node C is populated as device C. No cycles detected because cycle detection is only run when a fwnode link is converted to a device link.

2. Node B is populated as device B. As we convert B --> C into a device link we run cycle detection and find and mark the device link/fwnode link cycle:
C--> A --> B.EP ==> B --> C

3. Node A is populated as device A. As we convert C --> A into a device link, we see it's already part of a cycle (from step 2) and don't run cycle detection. Thus we miss detecting the cycle:
A --> B.EP ==> B --> A.EP ==> A

Looking at it another way, A depends on B in one way:
A --> B.EP ==> B

But B depends on A in two ways and we only detect the first:
B --> C --> A
B --> A.EP ==> A

To detect both of these, we remove the incorrect optimization attempt in step 3 and run cycle detection even if the fwnode link from which the device link is being created has already been marked as part of a cycle.

---
 drivers/base/core.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

index 52215c4c7209..e3d666461835 100644
@@ -2060,9 +2060,14 @@ static int fw_devlink_create_devlink(struct device *con,
 
 	/*
 	 * SYNC_STATE_ONLY device links don't block probing and supports cycles.
-	 * So cycle detection isn't necessary and shouldn't be done.
+	 * So, one might expect that cycle detection isn't necessary for them.
+	 * However, if the device link was marked as SYNC_STATE_ONLY because
+	 * it's part of a cycle, then we still need to do cycle detection. This
+	 * is because the consumer and supplier might be part of multiple cycles
+	 * and we need to detect all those cycles.
 	 */
-	if (!(flags & DL_FLAG_SYNC_STATE_ONLY)) {
+	if (!device_link_flag_is_sync_state_only(flags) ||
+	    flags & DL_FLAG_CYCLE) {
 		device_links_write_lock();
 		if (__fw_devlink_relax_cycles(con, sup_handle)) {
 			__fwnode_link_cycle(link);

2.43.0.594.gd9cf4e227d-goog

The links in a cycle are not all logged in a consistent manner or not logged at all. Make them consistent and log all the link in the cycles (even the child ==> parent dependency) so that it's easier to debug cycle detection code. Also, mark the start and end of a cycle so it's easy to tell when multiple cycles are logged back to back.

---
 drivers/base/core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

index e3d666461835..084d9648e254 100644
@@ -125,7 +125,7 @@ static void __fwnode_link_del(struct fwnode_link *link)
  */
 static void __fwnode_link_cycle(struct fwnode_link *link)
 {
-	pr_debug("%pfwf: Relaxing link with %pfwf\n",
+	pr_debug("%pfwf: cycle: depends on %pfwf\n",
 		 link->consumer, link->supplier);
 	link->flags |= FWLINK_FLAG_CYCLE;
 }

@@ -1945,6 +1945,7 @@ static bool __fw_devlink_relax_cycles(struct device *con,
 
 	/* Termination condition. */
 	if (sup_dev == con) {
+		pr_debug("----- cycle: start -----\n");
 		ret = true;
 		goto out;
 	}

@@ -1976,8 +1977,11 @@ static bool __fw_devlink_relax_cycles(struct device *con,
 	else
 		par_dev = fwnode_get_next_parent_dev(sup_handle);
 
-	if (par_dev && __fw_devlink_relax_cycles(con, par_dev->fwnode))
+	if (par_dev && __fw_devlink_relax_cycles(con, par_dev->fwnode)) {
+		pr_debug("%pfwf: cycle: depends on %pfwf\n", sup_handle,
+			 par_dev->fwnode);
 		ret = true;
+	}
 
 	if (!sup_dev)
 		goto out;

@@ -1993,6 +1997,8 @@ static bool __fw_devlink_relax_cycles(struct device *con,
 
 		if (__fw_devlink_relax_cycles(con,
 					      dev_link->supplier->fwnode)) {
+			pr_debug("%pfwf: cycle: depends on %pfwf\n", sup_handle,
+				 dev_link->supplier->fwnode);
 			fw_devlink_relax_link(dev_link);
 			dev_link->flags |= DL_FLAG_CYCLE;
 			ret = true;

@@ -2072,6 +2078,7 @@ static int fw_devlink_create_devlink(struct device *con,
 		if (__fw_devlink_relax_cycles(con, sup_handle)) {
 			__fwnode_link_cycle(link);
 			flags = fw_devlink_get_flags(link->flags);
+			pr_debug("----- cycle: end -----\n");
 			dev_info(con, "Fixed dependency cycle(s) with %pfwf\n",
 				 sup_handle);
 		}

2.43.0.594.gd9cf4e227d-goog